To begin with, you may want to learn how to kick flip before you try to do a casper flip as that is half of the trick. Try practicing it at a low speed as there is a lot of movement with your feet and this will help you keep control of the board. Now set your front foot on the two bolts in the front of your board and have your back foot square. Pop the board up like a normal kick flip, sliding your foot underneath the board as you flip it and when it is flipped over, spin the board back around with your foot and land on the board.